A Three-Dimensional Modeling of Photovoltaic Thermal Collector

Transcription

1 A hree-dimensional Modeling of Photovoltaic hermal Collector H. Ben cheikh el hocine*, K.ouafek**, F.Kerrour***, A. Khelifa****, I. abet*****, H, Haloui****** *Unité de Recherche Appliquée en Energie Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, Algeria **Unité de Recherche Appliquée en Energie Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, Algeria ***Laboratoire de Modélisation des Dispositifs à Énergies Renouvelables et Nanométriques, Département d électronique, Université frères Mentouri Constantine, 25000, Algeria. ****Unité de Recherche Appliquée en Energie Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, Algeria *****Unité de Recherche Appliquée en Energie Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, Algeria ******Unité de Recherche Appliquée en Energie Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, Algeria (bencheikh_80@yahoo.fr, khaledtouafek@yahoo.fr, f_kerrour@yahoo.fr, khelifa_karim@hotmail.fr, tabet21@yahoo.fr, haloui_h@uraer.dz Received: Accepted: Abstract- In order to obtain a high current efficiency a photovoltaic generator PV, it has been necessary to recuperate the heat dissipated by combination a PV to a thermal heating system. he heat exchanger is under the PV, thus cooling the cells back face. Such a system therefore improves the efficiency of the PV module while extracting useful heat calories heating. In this paper, a 3D model of a new PV collector has been implemented using the Comsol environment. A (FEM approach is used for the analysis of the thermal and electrical behavior of new absorber integrated for the PV collector which has as an advantage of a simple realization and to use a material of galvanised steel for it low cost compared to other configurations of PV/ hybrid collectors. Some results are presented the temperature of the PV collector decreases with the increasing flow rate, For a flow rate of about kg/s and irradiation of 1000W/m² and ambient temperature equal to C, the temperature reaches a value equal to C. he influence of mass flow rate in the PV collector demonstrate that the PV cell temperature decreases with the increasing mass flow rate and the increases until the flow rate reaches about m/s; it reaches a value equal to C and electrical power equal to after these values will be maintained at a relatively constants values. Keywords PV module, photovoltaic, Photovoltaic-thermal PV, finite element method, COMSOL. 1. Introduction he PV cell temperature increases by the absorbed solar radiation that is not converted into electricity causing a decrease in their efficiency; for monocrystalline and amorphous silicon solar cells the efficiency decreases by about 0.45% and 0.25% for every degree rise in temperature. Recpectively, depending on the module design [1]. to create the hybrid solar collector (PV, a PV panel is assembled with a thermal solar collector that can simultaneously produce two forms of energies (electric and

2 thermal. hese deferent energy systems were evaluated on several sides exegetic and economic [2, 3]. A major research and development work on the photovoltaic thermal (PV hybrid technology has been done since last 30 years. ill date many researchers have done a lot of work and numbers of studies have been carried out in designing, simulation, modeling, and testing of these systems. he different applications of PV on commercial level are there but it is still limited due to product reliability and cost. Important research is necessary in the area PV predominantly in the thermal design of the absorber and manufacturing, materials and coating selection, energy conversion efficiency, cost minimization, performance tests, and control a system reliability [4]. For their applications can be cited building integrated air PV system, solar air heating PV system, liquid PV collector, concentrator PV system and heat-pipe-based PV [5]. here are several types of PV collectors and they are classified with respect to the fluid used, shape of the collector and whether it s integrated into a building or not. Furthermore, existence of glazing on the collector is another factor that distinguishes a PV collector s characteristics [6]. Liquid type PV collectors, air type PV collectors, concentrating PV collectors and building integrated PV collectors are the four different types of PV collectors [7]. Ibrahim et al. [8] have presented new absorber design for the system. Saving energy efficiency increased by 73% to 81%. ouafek et al. A new design of the air hybrid solar collector have been manufactured and studied. It was found that it has presented better thermal and electrical. It has a thermal efficiency of 48% [9]. Li et al. have designed and tested a new static incorporated static CPC-PV/ system. he results show good agreement with the theoretical and experimental study to predict the optical efficiency under outdoor conditions. [10] Huang et al. have studied an integrated solar-thermal system (IPVS. he results indicate that the solar PV collector consisting of a corrugated polycarbonate panel can obtain an approximately 61.3% yield [11]. he results of performance analysis of both single and double-pass PV air systems in the steady-state; executed by Sopian et al. [12], show that the double-pass photovoltaic thermal solar system produces better performance than the single-pass module at a normal operational mass flow rate range. the modeling and simulation of the performance of PV water collector studied by Kalogirou [13], demonstrate that the mean annual efficiency of this system increases from 2.8% to 7.7% and in addition covers 49% of the hot water needs in a house, thus increasing the mean annual efficiency to 31.7%. A photovoltaic thermal collector was bluilded by Sandnes and Rekstad. hey evaluators found that the paste of solar monocrystalline silicon cells on the absorbing surface would reduce the solar energy absorbed by the module [14]. A thermal model for an integrated photovoltaic thermal solar system developed by iwari and Sodha was compared with the model of Huang et al. [15]. he simulations predicted a daily primary energy saving efficiency of around 58%, which was in good agreement with the experimental value (61.3% obtained by Huang et al. he scope of this paper is the analysis of new configuration for hybrid PV collector based on a new integrated absorber configuration using the Comsol environment. 2. heoretical Model he absorber of new configuration for hybrid PV collector is formed by two types of the first is parallel vertical tubes wherein the heat transfers fluid, and the second is an enclosure. he performances of collector is dependent on how they are arranged, i.e., on the flow rate through risers and on the inlet temperatures to individual modules. he design of collector modules is not the same; the performance of the prototype will not be the same. In the series arrangement, the performance of the second module will not be the same as the first as its inlet temperature will be the outlet temperature of the first. he outlet temperature of the water at the outlet of the collector in parallel vertical tubes PV given by fo1 becomes the inlet temperature to the collector whose PV absorber is an enclosure given by fi2, fi2 = fo1. 3. Numerical Modeling For water flowing through the tube, the energy balance of flowing water through duct tube is given by, Q [ S U ( ] u, 1 = A1 FR 1 1 L, 1 fi a (1 Where fi is the inlet temperature to the pair of collectors and fo1 is the inlet temperature to the second collector, which is found from the outlet of the first collector: = Qu,1. (2 m C fo1 fi + In the second case Q f ( S U ( u, 2 = A2 FR 2 2 L,2 fo, 1 where, A 1, A 2 are the collector area of first and second collector; a is the ambient temperature; he quantity F R is equivalent to the effectiveness of conventional heat exchanger, which is defined as the ratio of the actual heat transfer to the maximum possible heat transfer. a (3 385

3 U L,1 and U L,2 are the overall thermal loss efficient of first and second PV collector its value may be computed by using the concept of thermal network he value of a heat loss at the upper surface (1D model U L,1 and F R1 was calculated by, Formula of Klein (Duffie and Beckman, 1991, p. 260 [16]. he useful heat output from two combinations is given as: Q u, 1+ 2 = Qu,1 + Qu,2 (4 he thermal efficiency is given by Qu, 1+ 2 η = (5 A G. mc p ( fo fi η = (6 A G fi a η = ηth a (7 0 2 G. m is mass flow rate, Cp is specific heat capacity, η tho the zero loss efficiency for global radiation (G in W/m 2 at normal incidence, a is the ambient temperature,, and a 2 terms that describe the temperature-dependent heat losses. he electrical efficiency of a PV module represented by formulate of Schott [18] is given by: e = η c ref η (8 As is shown in the Eqt (8. η 0 is the reference efficiency of the solar cell at ref =20 C which is in our study 15%. 4. Analysis Using Comsol he Finite Element Method is the numerical technique applied by COMSOL for finding approximate solutions to boundary value problems. he three dimensional geometry of the new configuration of PV collector (shown in Fig. 1 developed in COMSOL was used simulations. Fig. 1. hree dimensional view of the geometry used in COMSOL. his section proposes the simulation steps for the thermal analysis of the proposed model. For each analysis, a brief summarization of the specific parameters and boundary settings is presented. he thermal analysis has been developed using the Comsol s Conjugate heat transfer module. In the Conjugate Heat ransfer Module, the following conditions were manually added to the model: Heat ransfer in Solids he collector consists of an assembly of elements which are: he transparent cover, amonocristallin s photovoltaic module, absorber, the insulation ensured by glass wool. Fluid COMSOL numerically solves the continuity and momentum equations, which are the governing equations for the fluid flow, and are shown below in equation (9 and equation (10, respectively. ( u = 0 ρ (9 ( ( u + ( u ρ u. u = p +. µ (10 he conduction-convection equation is also solved for the heat transfer in the flowing water, which is shown in Equation (11. ( k ρ u. =. (11 C p (K is fluid temperature, C p (J/kg K is the specific heat at constant pressure, ρ (kg/m 3 is the fluid density, u is the flow velocity (m/s, k (W/m K is the thermal conductivity. emperature = 0 (12 386

4 Outlet Outlet (Water flow exit, set to pressure, pressure = [1atm]; he collector was meshed in COMSOL using the built-in physics controlled mesh sequence setting. As shown in Fig. 2 below, the number of mesh elements increase at each boundary so that the heat transfer and flow fields can be resolved accurately, while ensuring that accurate results. Heat Flux 1 he heat flux (thermal flux is the rate of heat energy transfer through a unit of area in a given surface. he following equation was used in the heat flux interface in COMSOL: ( k 0 n. = q (13 he term q 0, which corresponds to the incoming flux, is set up equal to 1000W/m 2 ; Heat Flux 2 Is the convective contribution to the total flux, depends by the heat transfer coefficient h and the difference between the external temperature ext, and the unknown temperature. ( k = h ( n.. (14 ext he value of the initial external temperature has been set up equal to K while the h value has been computed equal to 17,8 W/m 2 K. Surface-to-Ambient Radiation 1 Is the radiative contribution to the total flux on the collector. ( 4 4 k =.( n. εσ (15 amb σ is the Stefan-Boltzmann constant, ε emissivity, and the amb represents the environment temperature. he material used for both the absorber plate and the tube is copper; the input parameters used in the analysis are shown in able I. able 1. Data used for simulation Fig. 2. hree dimensional view of the mesh used. 5. Experimental Study A. Materials Used Monocrystalline silicon for photovoltaic module. Galvanized steel tubes 12/17 Ø Galvanized steel tube 20/27 Ø wo sheets of galvanized steel [1mm-3mm] 20mm angle iron 30mm aluminum angle Polystyrene Glass wool Paintings (black and white. 6. Results and Discussion Layer λ(w/m.k C(J/Kg Rho(kg/m 3 Value Glass Cover PV Cell Layer of edlar / Absorber Plat (Steel / Insulation Meshing he simulations required good refinement of the finite elements in the mesh to acquire acceptable results. he new hybrid PV collector placed on the control structure Fig. 3. this photo taken in the laboratory of the Unit for Applied Research in Renewable Energy in Ghardaïa. Data acquisition of type (Data Acquisition/Switch Unit is used to determine the values of temperature. wo K- 387

5 type thermocouples are placed at two different points av1 and av2 to the front panel to confirm uniform distribution temperature on the front and a thermocouple placed on the rear panel to identify the assurance of perfect isolation av_pvt ar_pvt e_pvt s_pvt emperature ( C ime (hour Fig. 3. Photo of the new PV collector Calculations are done for typical day of November 2/11/2015 in the site of Ghardaïa; for a given design and climatic parameters. he variations of global solar radiation and ambient temperature for a typical day in the month of November 2015 of Ghardaïa site is shown in Fig. 4. he measure of solar intensity and ambient temperature are carried every two minutes in order to obtain a good accuracy for all measurements performed as temperature at different location. he experimental results are presented from following figure, we noted that variation of front face temperature of the collector was measured, it maximum value reached to 53,646 C. he outlet temperature of the fluid equal to 43,282 C, the maximum difference between inlet and outlet temperature of fluid equal to C observed at 12.29h which shows the gain in produced thermal energy for a ambient temperature equal to C. Solar radiation G(W/m² :03 10:03 11:03 12:03 13:03 14:03 15:03 16:03 17:03 ime (h G (W/m² amb Fig. 4. Hourly variation of solar intensity and ambient temperature for the day of 2/11/ Ambient temperature amb ( C Fig. 5. Experiment values of temperatures for each component of PV for 2/11/2015 A simulation with Matlab [17],was performed to predict the thermal efficiency of various PV-panels. Fig. 6 show thermal efficiency variations at different PV configurations, these results are referred to thermal efficiency of water η th in the mode of water heat exchanger; the ration Δ G (C W - 1 m² is the reduced temperature, with Δ = i a (K. he PV/ collector in PV with absorber in parallel vertical tubes is obviously performing more at zero reduced temperature; it was found to be 41.86% and 30% at PV in enclosure which represents a lower value. hermal efficiency New configuration tubes enclosure (fi - a/g ( Cm /W Fig. 6. Variations of the thermal efficiency according to the reduced temperature ( fi - a /G at various PV-panels. A new of design combined PV-thermal collector has been evaluated in software-comsol MULIPHYSICS, to investigate the thermal performance, it structure is obtained through the superposition of more layers cited above. Fig.8 illustrates 3 dimensional plots for the steady state solution of temperature profile of PV. he first step of simulation performed assume that the water inlet temperature was of uniform temperature equal to K (20 C, which is the same temperature specified for the ambient temperature and working fluid flow rate equal at kg/s presnted in Fig

6 he Fig. 9 shows the temperature distribution in new design of absorber for value of the wind speed equal to 1 m/s; the value of radiation 1000W/m 2, an ambient temperature of K (20 C, it found equal to C. he electrical energy of the PV Cell is presented in Fig.10. It can be observed that the electrical energy is linear function of module temperature. he electrical energy of PV module declines with the increase in temperature of the PV module, for a cell temperature equal to 25 C and reference temperature equal to 20 C the electricl power equal to 59 W. Numerical simulation (CFD can conduct a parametric sweep aims to clarify and quantify the evolution of various parameters such as temperature profile and electrical power depending on same parameters meteorological and physical (Irradiation G, mass flow rate involved in the study of the performance of our model. he mass flow rate range is ( m/s with a step of m/s. It influence in term of the temperature and electrical power of collector PV is presented in Fig.11 and Fig.12. he temperature of the PV cell decreases with the increasing mass flow rate until the flow rate reaches about m/s; it reaches a value equal to C after which it maintains at a relatively constant value. When the mass flow rate increases beyond m/s, the electrical efficiency of the novel design of collector will be maintained at a relatively constant level W, as shown in Fig.12. Explain that heat extracted by the cooling fluid has reached a saturated level and it cannot be increased further by increasing the mass flow rate. From the presented results of Fig. 13, it can be seen that the temperature and electrical power of PV collector increases when the solar radiation increases, for example, for an illumination of 600W/m 2, and ambient temperature equal to K for, the collector temperature reaches a maximum value equal to C, for flow rate equal to kg/s, keeping the other constant values. Fig. 8. emperature variation in the PV collector Fig. 9. emperature variation in new design of absorber. Fig.10. Electrical power as a function of PV cell temperature Fig.7. Velocity in the PV collector 389

7 7. Conclusion Fig.11. Influence of flow rate on the cell temperature of PV. We have presented the new configuration of hybrid collector (parallel vertical tubes - an enclosure. he aim is to increase the energy effectiveness of electric and thermal conversion with the lowest cost compared to the already existing conventional hybrid collector. Some results of this configuration has been presented; these clearly show the direct impact of various parameters, in particular the solar radiation and mass flow rate on the thermal and electrical parformances of the collector. the simulate results could be indicated that having a higher mass flow rate results in higher power production from PV Cell due to decreased its temperature, assists in keeping the PV Cell temperature at optimum value. he operating temperature of cell could be maintained at C and the electrical energy could also be kept at around W. he mass flow rate of kg/s is sufficient to absorb the maximum amount of heat from the PV cell. When the mass flow rate exceeds this value, the electrical energy is no longer affected. he integrated system could produce useful power augmenting power production from PV cell. References Fig.12. Electrical energy as a function of flow rate in the new PV collector A C Fig. 13. Influence of solar radiation and on the temperature and electrical power of PV collector. B D [1] Kalogirou, S.A., ripanagnostopoulos, Y.: Hybrid PV/ solar systems for domestic hot water and electricity production, Energy Convers. Manage, 2006, 47, pp [2] Agrawal, S., iwari, G.N.: Energy and exergy analysis of hybrid microchannel photovoltaic thermal module, Sol. Energy, 2011, 85, pp [3] Agrawal, S., iwari, G.N.: Overall energy, exergy and carbon credit analysis by different type of hybrid photovoltaic thermal air collectors, Energy Convers. Manage, 2013, 65, pp [4] A. Kumar and al. Historical and recent development of photovoltaic thermal (PV technologies. Renewable and Sustainable Energy Reviews 42 ( [5] Chow. A review on photovoltaic thermal hybrid solar technology. Appl Energy 2010;87: [6] PV Catapult, EU 6 th Framework. PV/ Roadmap. EU 6 th Framework Programme [7] Kalogirou, S.A. Photovoltaic thermal (PV/ collectors: A review: Elsevier, [8] Ibrahim A, Fudholi A, Sopian K, Othman MY, Ruslan MH. Efficiencies and improvement potential of building integrated photovoltaic thermal (BIPV system. Energy Convers Manage 2014;77: [9] ouafek K, Mourad H, Malek A. Design and modeling of a photovoltaic thermal collector for domestic air heating and electricity production. Energy Build 2013; 59:21 8. [10] Li G, Pei G, Yang M, Ji J, Su Y. Optical evaluation of a novel static incorporated compound parabolic 390

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